Cubic boron nitride flat cutting element compacts

ABSTRACT

Flat composite cutting elements are provided having a layer of Cubic Boron Nitride comprising less than 80 volume percent Cubic Boron Nitride sandwiched between two layers each made from a material brazeable to carbide or steel.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims priority on U.S. Provisional Patent Application No. 60/193,864 filed on Mar. 30, 2000, which is fully incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to flat cutting elements and more specifically to flat composite cutting elements having an ultra hard material layer, comprising less than 80 volume percent cubic boron nitride, sandwiched between two outer layers of material. Each of the two outer layers is be made from a material brazeable to carbide or steel.

BACKGROUND OF THE INVENTION

[0003] Flat cutting elements are used in drill blanks or shafts of flat drills or other cutting tools. Current flat composite elements containing an ultra hard material layer sandwiched between two layers of a refractory metal are typically brazed in drill blanks. Once the cutting element is brazed, the drill body may be fluted and shaped.

[0004] Typical flat composite elements comprise a layer of polycrystalline diamond sandwiched between two layer of a refractory metal. Other cutting elements have incorporated a central layer of cubic boron nitride (CBN) containing more than 80% by volume CBN and sandwiched between two layers of refractory metal. However, forming a flat cutting element using CBN central layer between two layers at least one of which is a carbide layer, as for example a Tungsten Carbide layer, has been avoided because the carbide layer tends to crack or delaminate from the CBN.

SUMMARY OF THE INVENTION

[0005] Flat composite cutting elements (also referred to herein as “compacts” or blades”) are provided for use in a drill blank or a shaft of a flat drill or other cutting tool. An exemplary embodiment inventive cutting element incorporates CBN sandwiched between two layers, each layer made from a material selected from the group comprising a carbide of a refractory metal selected from the groups IVB, VB, and VIB of the periodic table, or any metal that is brazeable to a carbide or steel, and any combinations thereof. Less than 80% by volume of CBN is used to form the CBN layer.

[0006] In a further exemplary embodiment, the flat cutting element comprises a layer of CBN sandwiched between a layer made from a material selected from the group comprising carbides of refractory metals from the groups IVB, VB, and VIB of the periodic table, and any combination thereof, and a layer of a refractory metal selected from the groups IVB, VB, and VIB of the periodic table as for example tungsten, niobium, tantalum or molybdenum. With this embodiment, less than 80% by volume of CBN may be used to form the CBN layer.

[0007] The CBN layer compositions may include second phase materials such as TiN, TiC, TiCN ranging from 0-45 volume percent and which have a C:N ratio less than or equal to 1. In addition 10-15 volume percent of the CBN layer composition may be a solution of AlN, AlB2 or Co-Wc. Moreover, the CBN layer compositions may include a binder phase in the range of 5% to 20% by volume.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a perspective view of a exemplary embodiment flat cutting element compact of the present invention.

[0009]FIG. 2 is a perspective view of the flat cutting element disclosed in FIG. 1 incorporated in a slot of a standard drill blank.

[0010]FIG. 3 is a cross-sectional view of a can including a stack of components for forming an exemplary embodiment cutting element of the present invention.

[0011]FIG. 4 is cross-sectional view of a can including a stack of components for forming alternate exemplary embodiment cutting element of the present invention.

[0012]FIG. 5 is a cross-sectional view of a can including a stack of components used to form a further exemplary embodiment cutting element compact of the present invention.

[0013]FIG. 6 is a cross-sectional view of a can including a stack of components used to form another exemplary embodiment cutting element compact of the present invention.

[0014]FIG. 7 is a cross-sectional view of a can including a stack of components used to form a further exemplary embodiment cutting element compact of the present invention.

[0015]FIG. 8 is a table depicting the feed compositions of various CBN grades for forming a CBN layer used of a cutting element of the present invention.

[0016]FIG. 9 is a cross-sectional view of another exemplary embodiment flat cutting element compact of the present invention.

DETAILED DESCRIPTION

[0017] The present invention relates to composite cutting elements and specifically to flat composite cutting elements which are also referred to herein as “compacts” or “blades”. Flat composite cutting elements are described in U.S. Pat. Nos. 4,906,528; 4,527,643; and 4,627,503 all three of which are fully incorporated herein by reference. In an exemplary embodiment, an inventive cutting element may be formed in any desired shape as for example a flat chevron shape for forming the tip of drill bit. In other exemplary embodiments, the inventive cutting element may be formed as a flat rectangular piece 10 (FIG. 1). The rectangular cutting element may be cut if necessary using EDM and other cutting methods to any desired shape.

[0018] The inventive cutting element incorporates an ultra hard material layer 16 comprising cubic boron nitride (CBN) sandwiched between two layers 18, 20 (FIG. 1) of less hard material. For convenience, the ultra hard material layer 16 is referred to herein as the “CBN layer”. The two layers of less hard materials are then brazed onto the slot of the appropriate blank, as for example the slot 12 of drill blank 14 shown in FIG. 2. Once the cutting element is brazed, the blank may be fluted and shaped. In an exemplary embodiment, the flat cutting element comprises a layer of CBN sandwiched between two layers of Tungsten Carbide. In another exemplary embodiment, the CBN layer is sandwiched between a layer of Tungsten Carbide and Cobalt on one side and another layer made of a material selected from the group comprising Tungsten Carbide, or any other carbide of a refractory metal selected from the groups IVB, VB, and VIB of the periodic table, and any combination thereof. It should be noted that groups IVB, VB and VIB of the periodic table referred to herein are the CAS version groups which correspond to groups IVA, VA and VIA, respectively in the IUPAC form of the periodic table.

[0019] In another exemplary embodiment, the CBN layer is sandwiched between two layers each made from a material selected from the group comprising carbides of refractory metals from the groups IVB, VB, and VIB of the periodic table, and any combination thereof. In a further exemplary embodiment, the flat cutting element comprises a layer of CBN sandwiched between a layer made from a material selected from the group of carbides of refractory metals from the groups IVB, VB, and VIB of the periodic table, and any combination thereof, and a layer of a refractory metal from the groups IVB, VB, and VIB of the periodic table, as for example a layer of Tungsten, Niobium, Tantalum or Molybdenum. In yet a further exemplary embodiment, the flat cutting element comprises a layer of CBN sandwiched between two layers each comprising a refractory metal selected from the groups IVB, VB and VIB of the periodic table. In another exemplary embodiment, the flat cutting element comprises a layer of CBN sandwiched between two layers each made from a material brazeable to carbide or steel.

[0020] The thickness ratio A:B (FIG.1) of a carbide layer to the CBN layer of a flat composite cutting elements of the present invention is in the range of about 9:1 to 36:1. The thickness ratio A:B of a refractory metal layer to the CBN layer of a flat composite cutting element of the present invention is in the range of 0.3:1 to 2.25:1.

[0021] Applicants discovered that they can produce a flat composite cutting element having a CBN layer sandwiched between two layers of Tungsten Carbide without cracking of the Tungsten Carbide layers or delamination of the Tungsten Carbide layers from the CBN layer, by forming the CBN layer with a volume content percentage of CBN that is less than 80%. By using a CBN layer formed with a volume content of CBN that is less than 80%, the modulus mismatch between the CBN layer and Tungsten Carbide layers is reduced thereby reducing the risk of cracking or delamination of the Tungsten Carbide layers. While reducing the volume percent content of the CBN reduces the hardness of the CBN layer, the reduction in the CBN content enhances the chemical stability of the CBN layer. In fact, applicants discovered that by being able to use a CBN layer having a volume percentage content of CBN of less than 80%, applicants were able to tailor the CBN layer to have chemical and thermal stability when the cutting element is used to cut different materials. Exemplary grades of CBN include applicant Megadiamond's MN-50 grade whose feed composition is depicted in FIG. 8. A feed composition is the composition a material prior to sintering. It is envisioned that the CBN layer may have a volume percentage of CBN that may be 40% or less. It should be notes that all volume percentages unless otherwise specified are volume percentages after sintering.

[0022] The CBN layer compositions used in the cutting elements of the present invention may include second phase materials such as TiN, TiC, TiCN ranging from 0-45 volume percent and which have a C:N ratio less than or equal to 1. In addition 10-15 volume percent of the CBN layer composition may be a solution of AlN, AlB2 or Co-Wc. Moreover, the CBN layer compositions may include a binder phase in the range of 5% to 20% by volume.

[0023] Applicants have also discovered that the risk of cracking and delamination to a Tungsten Carbide layer adjacent to CBN layer is decreased by using a refractory metal layer on the other side of the CBN layer, e.g., by sandwiching the CBN layer between the Tungsten Carbide layer and a refractory metal layer selected from the groups IVB, VB, and VIB of the periodic table, as for example, Tungsten, Niobium, Tantalum and Molybdenum. Applicants have discovered the residual stress distribution generated at the interface between the carbide layer and the CBN layer when the third layer is a refractory metal layer is not as conducive to the initiation of cracks when compared to the stress distribution generated at the interface between the Tungsten Carbide layer and the CBN layer when the third layer is also a carbide layer.

[0024] Because there are modulus and coefficient of thermal expansion mismatches between CBN and Tungsten Carbide, in any of the above references exemplary embodiments, a cobalt solution is infiltrated into the CBN composition which reduces the modulus mismatch between the resulting CBN composition and the Tungsten Carbide layer. This may be accomplished by using cobalt as the binder in forming the Tungsten Carbide layer. As a result the residual stresses generated at the interface between the CBN and Tungsten Carbide are reduced.

[0025] Another way to reduce the magnitude of the residual stresses generated at the interface between the central CBN layer and any of the adjacent layers is to make the interface between the CBN layer and its adjacent layer non-planar. An exemplary embodiment cutting element 10 of the present invention having non-planar interface 40 between the CBN layer 16 and a first outer layer 18, and having non-planar interface 42 between the CBN layer 16 and a second outer layer 20 is shown in cross-section in FIG. 9. The geometries of the interface may vary and may be formed with any of well known methods.

[0026] One way to form the cutting element compact is to use a can or cup which is made from a refractory metal selected from the groups IVB, VB and VIB of the periodic table, as for example, Tungsten, Niobium, Tantalum or Molybdenum. A typical can or cup 22 is shown in FIG. 3. A tungsten metal disk 24 is placed on the bottom 26 of the can. CBN powder with a binder and other appropriate constituents as for example set forth in FIG. 8, are then placed over the disk for forming a CBN layer 16. A preferred binder is AlN. The CBN layer 16 is covered by a layer 25, comprising Tungsten Carbide powder and a binder such as Cobalt. The Cobalt may be applied as a separate layer, as for example, a disc. The can is covered with a cover 30 and the entire assembly is then sintered under high pressure and temperature for forming a flat cutting element compact having a CBN layer sandwiched between a Tungsten layer and a Tungsten Carbide layer.

[0027] In an alternate exemplary embodiment shown in FIG. 4, the can itself is used to form one layer of the cutting element compact. For example, a Niobium can 22 may used to form a Niobium layer. With this embodiment, at least one disk of Niobium 34 is placed in the can over which is placed the CBN powder with appropriate constituents and binder for forming the CBN layer 16. A Tungsten Carbide powder with binder is then placed over the CBN layer for forming the carbide layer 25. The can is then covered with a cover 30 and the entire assembly is then sintered under high pressure and temperature whereby the Niobium can bottom 26 and Niobium disk 34 form a refractory metal layer of the cutting element.

[0028] In a further alternate embodiment shown in FIG. 5, the CBN powder with appropriate constituents and binder is placed directly on the refractory metal can bottom 24 for forming the CBN layer 16. The CBN powder is covered with Tungsten Carbide powder with binder for forming the carbide layer 25. The assembly is then covered with cover 30 and sintered. The sintered assembly is cut to remove portions of the sintered can such that the can bottom 26 forms a refractory metal, i.e., in this example a Niobium layer, which sandwiches the CBN layer 16 with a Tungsten Carbide layer. Alternatively, the carbide powder and binder is placed on the can bottom followed by the CBN powder and constituents. The can in the covered and sintered under high temperature and pressure. With this latter embodiment, the cover of the can forms a refractory material layer of the cutting element.

[0029] In yet a further exemplary embodiment shown in FIG. 6, CBN powder with appropriate constituents and binder for forming a CBN layer 16 is placed in the refractory metal can 22 and sintered. With this embodiment, portions of the can, as for example the can bottom and cover are used to form the two refractory metal layers sandwiching the CBN layer.

[0030] To form a cutting element of the present invention comprising a layer 16 of CBN sandwiched between two carbide layers, Tungsten Carbide powder and a Cobalt binder or a Tungsten Carbide disk and a Cobalt binder or Tungsten Carbide Cobalt disk is placed on the refractory metal can bottom 26 (FIG. 7). CBN powder with constituents and binder placed over the carbide powder. The CBN powder is then covered by Tungsten Carbide powder and binder. The assembly is then covered with cover 32 and sintered. Furthermore, with any of the aforementioned embodiments, instead of powder form, the CBN layer 16 may be in sheet form which may be preformed with the inclusion of a binder. If a carbide layer comprising a carbide of a refractory metal from the groups IVB, VB, and VIB of the periodic table or any combination thereof is desired then such carbide material may be substituted for forming the layer 25. The carbide layers may also be preformed in sheet form.

[0031] With any of the aforementioned embodiments, the sintered can assembly is cut to expose the cutting element.

[0032] Although the present invention has been described and illustrated to respect multiple embodiments thereof, it is to be understood that it is not to be so limited, since changes and modifications may be made therein which are within the full intended scope of this invention as hereinafter claimed. 

1. A cutting tool composite compact blade comprising: a first layer formed from a material selected from the group consisting of refractory metals and carbides of refractory metals selected from the groups IVB, VB and VIB of the periodic table; a second layer formed from a material selected from the group consisting of refractory metals and carbides of refractory metals selected from the groups IVB, VB and VIB of the periodic table; and a third layer of ultra hard between the first and second layers, wherein said third layer comprises less than 80% by volume CBN.
 2. A composite compact blade as recited in claim 1 wherein the first layer is formed from a refractory metal and wherein the second layer is formed from a material selected from the group consisting of carbides of refractory metals selected from the groups IVB, VB and VIB of the periodic table.
 3. A composite compact blade as recited in claim 1 wherein the first layer is formed from a material selected from the group consisting of carbides of refractory metals selected from the groups IVB, VB and VIB of the periodic table and wherein the second layer is formed from a material selected from the group consisting of carbides of refractory metals selected from the groups IVB, VS and VIB of the periodic table.
 4. A composite compact blade as recited in claim 1 wherein the first layer is formed from a refractory metal and wherein the second layer is formed from a refractory metal.
 5. A composite compact blade as recited in claim 1 wherein each of the first and second layer comprises a binder phase in the range of 5% to 20% by volume.
 6. A composite compact blade as recited in claim 1 wherein the third layer comprises less than 40% by volume CBN.
 7. A composite compact blade as recited in claim 1 wherein the third layer further comprises a material selected from the group of AlN, AlB₂ and Tungsten Carbide in the range of about 10% to 15% by volume.
 8. A composite compact blade as recited in claim 1 wherein the third layer further comprises a second phase material in the range of about 0 to 45% by volume.
 9. A composite compact blade as recited in claim 8 wherein the second phase material comprises a material selected from group consisting of TiN, TiC, and TiCN.
 10. A composite compact blade as recited in claim 8 wherein the second phase material comprises a C:N ratio not greater than
 1. 11. A composite compact blade as recited in claim 1 wherein the first layer comprises a thickness and wherein the third layer comprises a thickness and wherein the ratio of the thickness of the first layer to the thickness of the third layer is in the range of about 9:1 to about 36:1.
 12. A composite compact blade as recited in claim 1 wherein the third layer comprises a non-uniform face, facing toward the first layer.
 13. A composite compact blade as recited in claim 1 wherein the first layer comprises a non-uniform face facing toward the third layer.
 14. A composite compact blade as recited in claim 1 wherein the first and second layers each comprise a non-planar face, wherein the non-planar face of the first layer faces toward the non-planar face of the second layer.
 15. A composite compact blade as recited in claim 1 wherein the third layer comprises a first non-planar face facing toward the first layer and a second non-planar face opposite the first non-planar face facing toward the second layer.
 16. A method for making a composite compact blade comprising a CBN layer sandwiched between a refractory metal layer and a carbide layer, the method comprising the steps of: providing a can made from a refractory metal the can having an open end and a cover; placing a layer of CBN in the can; covering the can open end with the cover forming an assembly; and sintering the assembly for forming the cutting element having a CBN layer and another layer formed by a portion of the can.
 17. A method as recited in claim 15 further comprising the step of cutting the sintered assembly to remove portions of the sintered can.
 18. A method as recited in claim 15 wherein another portion of the can forms another layer of refractory metal, wherein the two refractory metal layers sandwich the CBN layer.
 19. A method as recited in claim 15 further comprising the step of providing a layer of a carbide material between the can and the CBN layer, the carbide material selected from the group consisting of carbides of a refractory metals selected from the groups IVB, VB and VIB of the periodic table.
 20. A method as recited in claim 15 wherein the refractory metal can comprises a material selected from the group consisting of refractory metals selected from the groups IVB, VB and VIB of the periodic table. 